1. Field of the Invention
The present invention relates to an image forming apparatus which receives image data and prints it out with printing substance such as ink. One example of such an image forming apparatus is an ink-jet printer in which each ink nozzle of a group of ink nozzles provided in a print head jets ink drops on a paper sheet and thus prints an image. Another example of the image forming apparatus is a facsimile apparatus using such an ink-jet printer. The facsimile apparatus receives an image signal and then once stores image data carried by the image signal in image data storing means. After the image signal reception has been terminated, the image data thus-stored in the image data storing means is used to print out relevant images.
2. Description of the Related Art
Such a facsimile apparatus using the ink-jet printer is advantageous in view of quietness in operation thereof, a overall size thereof and a cost thereof. Further, an image printed out from the facsimile apparatus on a paper sheet is well preserved in comparison to a facsimile apparatus using a thermal printer. Further, the facsimile apparatus using the ink-jet printer can provide a relatively high resolution, high quality printed image.
The ink-jet printer needs feeding ink appropriately. A problem in the ink-jet printer is a matter as to when the ink-jet printer needs feeding ink. One method of detecting a time the ink-jet printer needs feeding ink is to measure a weight of a ink tank and thus to measure how much ink remains in the tank. According to the method, when the thus-measured weight of the ink tank is lighter than a predetermined value, it is determined that it is a time the ink-jet printer needs feeding ink.
In another method, a number of black pixels which the printer has processed so as to print out images using the black pixels is counted. According to the method, when the thus-counted number exceeds a predetermined value, it is determined that it is a time the ink-jet printer needs feeding ink.
These methods have problems described below. In the former method measuring the ink tank weight, it is necessary that a high accuracy measuring instrument is used in order to obtain an accurate time the ink-jet printer needs feeding ink. However, such a size of a high accuracy measuring instrument is large and thus the facsimile apparatus becomes larger. Therefore, ordinarily, a weight measuring instrument not having a high accuracy is used there. As a result, an accurate time the ink-jet printer needs feeding ink cannot be obtained and thus it may be determined that it is a time the ink-jet printer needs feeding ink even when a substantially large amount of ink remains in the ink tank. If the determination is made that it is a time the ink-jet printer needs feeding ink, ordinarily, the ink tank present in the facsimile apparatus is replaced by a new ink tank. Due to such a not accurate determination of a time the ink-jet printer needs feeding ink, ink tank replacement operations are performed more frequently than are actually needed. Thus, running costs of the facsimile apparatus become higher.
In the latter method counting the number of black pixels, relationship between the thus-counted number of black pixels and an actual ink consumption may vary depending on environmental factors such as ambient temperature and/or humidity. Therefore, it is difficult to obtain an accurate ink consumption from the counted number of black pixels. Thus, it is difficult to obtain an accurate time the ink-jet printer needs feeding ink.